The present invention relates to a device for determining the corrosion of the grinding bodies in a rotary mill comprising a cylindrical shell ring revolving about its longitudinal axis and containing a grinding charge consisting of grinding bodies made of metal alloy, the mill having the material that is to be milled pass longitudinally through it.
The invention is aimed more specifically at the field of wet mills, particularly those used in the mining industry for crushing and grinding ores or in the cement-making industry. These mills contain a grinding charge consisting of grinding bodies such as balls, cylindrical pebbles, spherical pebbles, etc., and grinding occurs as the mill rotates under the effect of knocks and friction with the grinding charge and produces a kind of wet pulp.
These grinding bodies experience significant wear and their frequent replacement has a significant impact on the cost of grinding. It is therefore obvious that there is a need to monitor this wear so as to be able to choose appropriate alloys for the grinding bodies and to adapt the running conditions of the mill in order to lengthen the service life of the grinding bodies as far as possible and reduce the running costs of the mills.
Grinding body wear is a complex phenomenon to which essentially mechanical wear and corrosion contribute. Mechanical wear is brought about by abrasion and by the knocks and impacts, while corrosion is an electrochemical phenomenon which occurs in an aqueous medium under the effect of anode and cathode reactions. It is has been found that these various phenomena which are responsible for the overall wear of the grinding bodies have a synergic effect, that is to say that the overall wear is greater than the sum of the wear generated by the various individual phenomena which cause it. In other words, the corrosion of a grinding body which is subjected to mechanical wear may be greater than that of the same grinding body in the absence of mechanical wear, and vice versa.
Until now all that was done about corrosion wear was to observe it and make do with choosing materials and alloys best able to resist it, because there was no means for reliably determining the state and evolution of the corrosion of the grinding bodies while the mill was in operation. This is because the phenomenon of corrosion of the grinding bodies depends on several factors such as the composition and the nature of the alloy of the grinding bodies, the nature of the material being ground (e.g. iron ores or copper ores) the pH of the pulp, etc.
It is an object of the present invention to fill this gap and to provide a device for determining the corrosion of the grinding bodies during the grinding operation which is reliable enough to be able to optimize the grinding conditions and improve the conditions of wear of the grinding charge.
In order to achieve this objective, the present invention provides a device of the kind described in the preamble which is characterized in that at least one grinding body identical to those that make up the grinding charge is fixed to an elastomer or rubber pedestal, itself fixed to the interior surface of the shell ring, and in that this grinding body is exposed to the conditions inside the mill and is associated with a reference electrode from which it is electrically insulated, in that the said reference electrode is protected from impacts and knocks of the charge in the mill but is in electrical contact with the pulp in the mill and in that the said grinding body and the said electrode are electrically connected to measurement apparatus fixed outside the shell ring of the mill.
Each grinding body is preferably fixed to the pedestal and to the shell ring using a hollow bolt passing radially through the pedestal and the shell ring and containing the reference electrode which is bathed in an electrolyte in electrical contact with the pulp in the grinder. The hollow of the bolt may be closed at the interior end by a spongy plug projecting the reference electrode from knocks and allowing contact with the pulp.
The pedestal carrying the grinding bodies and the reference electrodes is preferably fixed on the inside of an inspection hatch, each mill being equipped with at least one of these hatches.
The measurement apparatus makes it possible to measure potential and/or current on each grinding body and its reference electrode and sends the data, telematically, to a receiving module remote from the mill. This module processes and analyses the data, the results of which provide indications regarding the corrosion of the grinding body on which the measurement was made.